1. Field of the Invention
The present invention relates generally to a batch type heat treatment system for collectively heat-treating a large number of objects to be processed, such as semiconductor wafers. More specifically, the invention relates to an adaptive controlled batch type heat treatment system for estimating the temperatures of semiconductor wafers, which are housed therein, to carry out the optimum control on the basis of the estimated results, a method for controlling the system, and a heat treatment method using the system.
2. Description of Related Background Art
As batch type heat treatment systems for collectively carrying out a heat treatment, such as deposition, oxidation or diffusion, with respect to a large number of semiconductor wafers, horizontal heat treatment systems and vertical heat treatment systems are known. Recently, vertical heat treatment systems are being mainly used on the grounds that the amount of the drawn atmosphere is small and so forth.
FIG. 5 shows the appearance of a vertical heat treatment system. This system comprises a vertical heating furnace 11 and a wafer boat 12 serving as a wafer holder. The heating furnace 11 comprises a heater which is provided around a vertical reaction tube. The heating furnace 11 is connected to a gas supply pipe 11a and an exhaust pipe 11b. 
The wafer boat 12 comprises a plurality of struts 13 having grooves in which the peripheral portions of a large number of wafers W are supported so that the wafers W are held at regular intervals in the form of shelves. After the wafer boat 12 supports the large number of wafers W, the wafer boat 12 is carried in the heating furnace 11 through a bottom opening of the heating furnace 11, and a predetermined heat treatment is carried out with respect to the wafers W.
In a control system for such a heat treatment system, process conditions (target values of process parameters), such as a process pressure, a process temperature and a gas flow rate, have been determined in accordance with, e.g., the kind and thickness of a thin film to be deposited, and a plurality of recipes in which these process conditions have been written have been prepared. If each operator selects one of the recipes in accordance with the kind and thickness of a thin film, the heat treatment system is operated on the basis of predetermined process conditions. Such recipes are prepared by actually fully loading wafers W in the wafer boat 12, carrying out a heat treatment and finding the optimum process conditions.
Recently, various semiconductor devices are required. Therefore, there are some cases where it is required to carry out a heat treatment with respect to a small lot of wafers of various kinds. For example, when it is required to process 150 product wafers as the full number (the full load number) of wafers, the wafer boat 12 is in a full load state. There are some cases where it is required to heat-treat a smaller number of wafers than the full load number, e.g., 100, 50 or 25 wafers. In such cases, a short number of dummy wafers are used for fully loading wafers in the wafer boat 12 to carry out a heat treatment on usual process conditions during the wafer full load.
Since the dummy wafers are expensive, the dummy wafers are cleaned every a plurality of processes to be repeatedly used. However, the dummy wafers are finally discarded to cause the rising of running costs.
Although the number of product wafers is small, it takes a lot of time to transfer dummy wafers, so that it is also a waste of time from the point of through put.
When the batch size is small (when the number of product wafers is smaller than the full number), if the process is carried out without the need of dummy wafers, an empty region in which no wafer is loaded exists in the wafer boat 12. In this case, the temperature of the wafers and the concentration of gas are partially disturbed to vary the wafer inplane uniformity, interplane uniformity and process speed in the heat treatment to deteriorate the repeatability of the heat treatment.
A typical batch type heat treatment system is designed to collectively process a large number of wafers. Therefore, it is not possible to finely control the process, so that there are some cases where wafer interplane and inplane variations are caused.
Conventionally, when wafers W and dummy wafers are fully loaded in the wafer boat 12 to heat-treat the wafers W, the temperature in the heat furnace 11 is measured to control the heater on the basis of the measured results. That is, conventionally, the temperatures of the wafers W themselves are not estimated in time series, and the heater is not controlled on the basis of the measured results so that the temperatures of the wafers W approach the target temperature values of the wafers W themselves. Therefore, conventionally, there is a problem in that it is not possible to precisely control the temperatures of the wafers W.
It is therefore an object of the present invention to eliminate the aforementioned problems and to provide a batch type heat treatment system capable of carrying out a good process even if a holder has an empty region in which no object to be processed is held, a method for controlling the heat treatment system, and a heat treatment method using the heat treatment system.
It is another object of the present invention to provide a batch type heat treatment system suitable for a multi-product small-lot production, a method for controlling the heat treatment system, and a heat treatment method using the heat treatment system.
It is a further object of the present invention to provide a batch type heat treatment system capable of suitably processing each of wafers even if the system is a batch type, a method for controlling the heat treatment system, and a heat treatment method using the heat treatment system.
In order to accomplish the aforementioned and other objects, according to a first aspect of the present invention, a batch type heat treatment system comprising: a heating furnace for housing therein objects to be processed; a plurality of heaters which are arranged for heating each of a plurality of regions of said heating furnace; a plurality of temperature sensors for detecting the temperature of each of said plurality of regions; a memory for storing therein a plurality of temperature estimating models, which have been prepared in accordance with the number and arranged position of said objects, for estimating the temperatures of said objects in said heating furnace, on the basis of outputs of said plurality of temperature sensors; and
a controller for selecting a temperature estimating model corresponding to information on the number and arranged position of said objects to be housed in said heating furnace, from said plurality of temperature estimating models to estimate the temperatures of said objects from the outputs of said plurality of temperature sensors on the basis of the selected temperature estimating model, and for controlling said plurality of heaters so that the temperatures of said objects reach target temperature values in accordance with the estimation of the temperatures of said objects.
With this construction, model storing means stores therein a temperature estimating model according to the processed number and arranged position of the objects to be processed. By the outputs of the plurality of temperature sensors and the temperature estimating model, the temperatures of the objects can be estimated. That is, the temperatures of the objects themselves can be indirectly measured. By controlling the plurality of heaters in accordance with the estimated temperatures, heating and cooling can be carried out so that the variation in temperature of each of the wafers is appropriate.
Therefore, the objects can be appropriately and precisely heated regardless of the number and arrangement of the objects.
The temperature estimating model may have a plurality of sub-models for controlling the heaters while estimating the temperatures of the objects, in order to cause the estimated temperatures of the objects to approach the target temperature values.
The sub-models are set every temperature zone, and said controller selects one of said sub-models according to the temperatures of said objects.
The controller has a recipe memory for storing a temperature recipe indicative of a time-varying temperature pattern which is to be applied to said objects, and said controller estimates the temperatures of said objects on the basis of the selected temperature estimating model so that the temperatures of said objects vary in accordance with said temperature recipe stored in said recipe storing means, and controls said plurality of heaters in accordance with the estimated temperatures of said objects.
The recipe memory stores therein a plurality of temperature recipes which are prepared every number and arranged position of said objects, and
said controller selects a temperature recipe corresponding to information on the number and arranged position of said objects to be housed in said heating furnace, from said plurality of temperature recipes to control said plurality of heaters in accordance with the selected temperature recipe.
The space in said heating furnace is divided into a plurality of partial zones in arranged directions of said objects, said temperature recipe comprises a plurality of sub-recipes which are prepared every one of said plurality of partial zones which are obtained by dividing the space in said heating furnace in the arranged directions of said objects, and
said controller controls said plurality of heaters in accordance with said sub-recipes corresponding to each of said partial zones.
The controller controls said plurality of heaters so that the difference between a set of wafer temperatures, which have been estimated referring to said temperature estimating models, and a set of temperatures, which are indicated by said sub-recipes of said plurality of partial zones, is minimum.
The information on the number and arranged position of said objects is inputted from an operation panel.
The information on the number of said objects is automatically acquired by a number counter for counting the number of said objects.
According to a second aspect of the present invention, there is provided a method for controlling a batch type heat treatment system comprising a furnace for housing therein objects to be processed, a plurality of heaters which are arranged for heating each of a plurality of regions of said heating furnace, and a plurality of temperature sensors for detecting the temperature of each of said plurality of regions, said method comprising: a model storing step of storing therein a plurality of temperature estimating models, which have been prepared in accordance with the number and arranged position of said objects, for estimating the temperatures of said objects in said heating furnace from the outputs of said plurality of temperature sensors; an information acquiring step of acquiring information on the number and arranged position of said objects to be housed in said heating furnace; a temperature estimating step of selecting a temperature estimating model corresponding to the acquired information, from said plurality of temperature estimating model to estimate the temperatures of said objects from the outputs of said plurality of temperature sensors on the basis of the selected temperature estimating model; and
a heater control step of controlling said plurality of heaters in accordance with the estimation of the temperatures of said objects so that the temperatures of said objects equal target temperature values.
Each of said temperature estimating models has a plurality of sub-models for controlling the heaters while estimating the temperature of the objects, in order to cause the estimated temperatures of said objects to approach said target temperature values, and said sub-models are set every temperature zone, and
said temperature estimating step selects one of said sub-models corresponding to the temperatures of said objects.
The space in said heating furnace is divided into a plurality of partial zones in arranged directions of said objects, said temperature recipe comprises a plurality of sub-recipes which are prepared every one of said plurality of partial zones which are obtained by dividing the space in said heating furnace in the arranged directions of said objects, and
said heater control step controls said plurality of heaters in accordance with said sub-recipes corresponding to each of said partial zones.
The heater control step controls said plurality of heaters so that the difference between a set of wafer temperatures, which have been estimated referring to said temperature estimating models, and a set of temperatures, which are indicated by said sub-recipes of said plurality of partial zones, is minimum.
According to a third aspect of the present invention, there is provided a heat treatment method using a batch type heat treatment system having a furnace for housing therein objects to be processed, a plurality of heaters which are arranged for heating each of a plurality of regions of said heating furnace, and a plurality of temperature sensors for detecting the temperature of each of said plurality of regions, said heat treatment method comprising: a model reading step of selecting and reading a temperature estimating model corresponding to information on the number and arranged position of said objects housed in said heating furnace, from a model memory for storing therein a plurality of temperature estimating models, which have been prepared in accordance with the number and arranged position of said objects, for estimating the temperatures of said objects in said heating furnace; a recipe reading step of reading a temperature recipe corresponding to the kind of a heat treatment, which is to be carried out with respect to said objects, from a recipe memory for storing therein a plurality of temperature recipes indicative of a time-varying temperature pattern which is to be applied to said objects; a temperature estimating step of estimating the temperatures of said objects from the outputs of said plurality of temperature sensors on the basis of the temperature estimating model which has been read at said model reading step; and
a heater control step of controlling said plurality of heaters so that the temperatures of said objects estimated at said temperature estimating step equal target temperature values indicated by the read temperature recipe.
Each of said temperature estimating models has a plurality of sub-models for controlling the heaters while estimating the temperature of the objects, in order to cause the estimated temperatures of said objects to approach said target temperature values, and said sub-models are set every temperature zone, and
said model reading step selects one of said sub-models corresponding to the temperatures of said objects.
Furthermore, mathematical models for executing the above described batch type heat treatment system controlling method and heat treatment method may be stored in ROMs, flash memories and so forth to be mounted in the batch type heat treatment system or distributed.